Human Body
Organ systems and how the body works.
Body
How the Heart Pumps Blood: Chambers, Valves and the Cardiac Cycle
How the four heart chambers, one-way valves and electrical pacemaker cells move blood through the lungs and body, explained step by step.
BodyHow the Kidneys Filter Blood: Nephrons, Reabsorption and Urine
How each kidney's million nephrons filter blood, reclaim water and nutrients, and remove waste to form urine, explained step by step.